On the reliability of analytical models to predict solute transport in a fracture network

Abstract

Abstract. In hydrogeology, the application of reliable tracer transport model approaches is a key issue to derive the hydrodynamic properties of aquifers.Laboratory-and field-scale tracer dispersion breakthrough curves (BTC) in fractured media are notorious for exhibiting early time arrivals and late time tailing that are not captured by the classical advection-dispersion equation (ADE). These "non-Fickian" features are proven to be better explained by a mobile-immobile (MIM) approach. In this conceptualization the fractured rock system is schematized as a continuous medium in which the liquid phase is separated into flowing and stagnant regions.The present study compares the performances and reliabilities of the classical MIM and the explicit network model (ENM), taking expressly into account the network geometry for describing tracer transport behavior in a fractured sample at bench scale. Though ENM shows better fitting results than MIM, the latter remains still valid as it proves to describe the observed curves quite well.The results show that the presence of nonlinear flow plays an important role in the behavior of solute transport. First, the distribution of solute according to different pathways is not constant, but it is related to the flow rate. Second, nonlinear flow influences advection in that it leads to a delay in solute transport respect to the linear flow assumption. However, nonlinear flow is not shown to be related with dispersion. The experimental results show that in the study case the geometrical dispersion dominates the Taylor dispersion. However, the interpretation with the ENM shows a weak transitional regime from geometrical dispersion to Taylor dispersion for high flow rates. Incorporating the description of the flow paths in the analytical modeling has proven to better fit the curves and to give a more robust interpretation of the solute transport.

Roughness scale dependence of the relationship between tracer longitudinal dispersion and Peclet number in variable‐aperture fractures

“…Many studies (Cherubini, Giasi, & Pastore, ; Cherubini, Giasi, & Pastore, ; Dou & Zhou, ) showed that the transport could be non‐Fickian in rough fractures with the heterogeneous flow field. The continuous time random walk (CTRW) model has been proven to be valid even in the non‐Fickian transport regime.…”

Computing Localized Breakthrough Curves and Velocities of Saline Tracer from Ground Penetrating Radar Monitoring Experiments in Fractured Rock

“…The BTC shape seems to indicate at least two arrivals and therefore two flow paths, an early one forming the peak and quick decrease afterwards (due to the transported formation water that was injected after the tracer), and a second one which seems to arrive later (approximately t = 90 min) and thus slowing down the decrease (by still transporting highly conductive tracer). Additional flow paths to explain the long tailing in the curve are possible, as can be expected for fractured flow systems (e.g., [46,47]). The form of the sensor BTC is comparable with results from Kittilä et al [43] and the multi-flow-path assumption is also in agreement with this publication, where data for a dye tracer that was injected during this experiment were evaluated.…”

Numerical modeling of flow and transport in the Bari industrial area by means of rough walled parallel plate and random walk models

“…where r w (L) represents the well radius, r SKIN (L) the radius of the damage zone, and R (L) the radius of influence of the well. The total drawdown is formed from three components: the hydraulic component of the aquifer assuming a valid Thiem function, a skin function presented by Cooley and Cunningham (1979) assuming that the transmissivity and the radius of the damage zone are, respectively, equal to T SKIN = T /2 e r SKIN = 2r w , and a contribution related to nonlinear losses introduced by Wu (2001).…”